Ferroelectric materials are used in a variety of applications. One such application is a ferroelectric capacitor used in a nonvolatile, random access memory whose information is retained even after a power loss. A ferroelectric material is one whose physical state changes upon the application of an electrical field, in a manner analogous with the change undergone by ferromagnetic materials to which a magnetic field is applied. A memory cell may be constructed based upon the hysteresis effects associated with the physical state change. The ferroelectric material has the advantages that its physical state is controlled by the application of a voltage rather than a magnetic field, a measurable state is retained after a power loss, and small-size memory elements may be constructed by microelectronics fabrication techniques, resulting in memory elements that consume little power.
One difficulty with using ferroelectric materials in some applications of interest, such as ferroelectric nonvolatile memory, is that some of the material properties such as permittivity change substantially over relatively narrow temperature ranges. These properties change so greatly, in some cases more than 100 percent over a temperature range of less than 100° C., that the associate read/write electronics can be quite difficult to design and implement.
Ferroelectric materials such as barium titanate, strontium titanate, calcium titanate, calcium stannate, and calcium zirconate are also used to produce discrete ceramic capacitors. For the discrete capacitor application, the material composition is varied to provide a relatively high permittivity over a specified temperature range. While these devices are optimized to provide a relatively constant capacitance value over a specified temperature range, they are not useful to non-volatile memory applications due to their lack of a remnant polarization component which can be used for information storage.
There exists a need for an improved approach to the design of electronic circuits that utilize ferroelectric properties, to reduce the effects of temperature variations. The present invention fulfills this need, and further provides related advantages.